This invention relates to a Wankel type rotary engine and more specifically relates to an improved rotary engine which exhibits superior thermal performance which may result in a lightweight, more efficient rotary engine.
The Wankel rotary engine is a type of internal combustion engine, invented by German engineer Felix Wankel, which uses a rotor instead of reciprocating pistons. This design delivers smooth high-rpm power from a compact, lightweight engine.
Referring to FIGS. 1A through 1D, in the Wankel engine 10, the four strokes of a typical Otto cycle occur in the space between a rotor 22, which is roughly triangular, having faces denoted ‘a’, ‘b’ and ‘c’, and the inside of a rotor housing 12. In the basic single-rotor Wankel engine, the oval-like epitrochoid-shaped inner surface 11 surrounds the three-sided rotor 22. Due to thermal requirements of the housing 12, most housings of the prior art are made from heavy sections of high strength aluminum. This typically results in a large, heavy and structurally inefficient housing 12. The central drive shaft 24, also called an eccentric shaft or E-shaft, passes through the center of the rotor and is supported by bearings (not shown). The rotor 22 both rotates around an offset lobe (crank) on the shaft 24 and makes orbital revolutions around the shaft 24. Apex seals 15 at the corners of the rotor 22 seal against the inner surface 11 of the housing, dividing it into three moving combustion chambers. As the rotor 22 rotates and orbitally revolves, each face ‘a’, ‘b’, and ‘c’ of the rotor 22 gets closer and farther from the surface 11 of the housing, compressing and expanding the combustion chamber similarly to the strokes of a piston in a reciprocating engine. The power vector of the combustion stage goes through the center of the offset lobe.
While a four-stroke piston engine makes one combustion stroke per cylinder for every two rotations of the crankshaft (that is, one half power stroke per crankshaft rotation per cylinder), each combustion chamber in the Wankel rotary engine generates one combustion stroke per each driveshaft rotation, i.e. one power stroke per rotor orbital revolution and three power strokes per rotor rotation. Thus, power output of a Wankel engine is generally higher than that of a four-stroke piston engine of similar engine displacement in a similar state of tune and higher than that of a four-stroke piston engine of similar physical dimensions and weight. Wankel engines also generally can operate at a higher RPM than a reciprocating engine of similar size since the strokes are completed with a rotary motion as opposed to a reciprocating engine which must use connecting rods and a crankshaft to convert reciprocating motion into rotary motion.
One well known drawback associated with the Wankel rotary engine is due to the fact that unlike a piston engine, where the cylinder is cooled by the incoming charge after being heated by combustion, Wankel rotor housings are constantly heated on one side and cooled on the other, leading to high local temperatures and unequal thermal expansion. This places high demands on the materials used, usually resulting in a rotor housing that is designed primarily to withstand the thermal environment which results in a heavy, structurally inefficient rotor housing.
As can be seen, there is a need for an improved rotary engine housing that provides for a more structurally efficient design while maintaining the advantages of the rotary engine.